This invention relates to ejector compressors and compressor-expanders, in particular, to their application to environmentally beneficial and energy efficient technologies in air-cycle refrigeration and power generation, turbo-chargers, and fuel-cell pressurization.
During the course of the 20th Century, science and engineering have brought us to an era whereby every American enjoys the availability of abundant energy as well as advanced technology for heating and air-conditioning of homes, transportation, and industry. Nevertheless, these wonders of modem society have come at a severe price to our global environment and to our reserves of non-renewable natural resources. Fossil fueled electrical power generation and automobiles have increased the level of carbon dioxide in the atmosphere to the point where deleterious global warming effects on the environment are predicted. Furthermore, due to the release of chlorofluorocarbons (CFC""s) from conventional refrigeration and air conditioning systems, the ozone layer protecting the earth from deadly ultraviolet radiation is being depleted, with serious projected consequences for mankind. This crisis is considered so serious that 159 nations, including the United States, met in Kyoto, Japan in December of 1997 and signed a treaty designed to limit the buildup of carbon dioxide and other greenhouse gases in our environment. Immediately following the signing of the treaty, there was an outpouring of concern that meeting the targets outlined in Kyoto would be impossible without either modifying radically the American way of life, or of finding new energy-efficient and non-polluting technologies.
In FIG. 10 is shown a conventional ejector which is well known in the prior art. This pumping device has the advantage of extreme simplicity, there being no moving parts. The principle of operation is that the high energy primary fluid entering the ejector through primary fluid inlet conduit 2, passes through a supersonic nozzle 5, and emerges therefrom as a high speed jet. Upon exiting said supersonic nozzle, the primary jet entrains secondary fluid introduced through a secondary fluid inlet conduit 3 into a plenum 24 through the action of turbulent mixing between primary and secondary fluid. The primary fluid expands and imparts energy to the secondary fluid through turbulent shear forces generated in the mixing process. The mixing and subsequent diffusion is controlled by aerodynamic shroud 10 and the mixed flow is discharged from the ejector at mixed-fluid outlet conduit 4. It may thus be seen that an ejector is a compressor-expander characterized by direct-contact between primary and secondary fluids and with a common discharge. The advantage of such direct-fluid-contact devices is the extreme simplicity and consequent low cost and low space consumption and low weight in comparison with indirect-fluid-contact compressor-expanders. The conventional ejector, as a result of its simplicity, finds application in numerous technologies. Nevertheless, it suffers from low efficiency as a result of the inherent irreversibility of the mechanism with which it operates: turbulent mixing. Despite a century of research on improving this device, its performance is limited by the nature of the physics of its operation.
Yet another disadvantage of the conventional ejector is that although energy is exchanged between primary fluid and secondary fluid, the said primary and secondary fluids are irreversibly mixed at said common discharge. In fact, research in improving conventional ejectors has generally focused on enhancing mixing between primary and secondary fluids. While for many applications, this is acceptable, it has precluded the use of ejectors in applications requiring minimal mixing of primary and secondary fluid streams and separation of the flows at discharge. For such applications, primary and secondary flows must be discharged diffluentially. For such applications requiring diffluential discharge, conventional compressors and expanders are used whereby a compressor is mechanically driven by an expander, and the primary and secondary flows do not mix. These machines are called xe2x80x9ccompressor-expandersxe2x80x9d and generally utilize expanders and compressors which individually operate as either positive displacement machines such as piston-type reciprocating, lobe, or twin-screw compressors or motors, and turbomachines such as turbines and centrifugal compressors. A typical prior art compressor-expander is shown in FIG. 22. It can be seen that the primary fluid stream is applied through inlet conduit 2 to the expander 83, and is discharged through outlet conduit 72. The secondary fluid is applied through inlet conduit 3 to the compressor 84 and is discharged separately through outlet conduit 74. Compressor 84 is driven through shaft 85 by expander 83. In this case, each fluid stream maintains its integrity with diffluential discharges and no combining takes place unless special provision is made by design. Such compressor-expanders are used in many applications of commercial or industrial importance. For example, compressor-expanders are used for fuel cell pressurization, turbo-charging internal combustion engines, and for air-cycle heat pumps.
According to xe2x80x9cFuel Cellsxe2x80x9d by McDougall, John Wiley and Sons,1976, page 78, the first successful working fuel cell was produced by F. T. Bacon in 1957. This fuel cell had a working temperature of 200xc2x0 C. and a pressure of 20-40 atm. For all fuel cells, the well known Nernst equation predicts that the output voltage of a fuel cell should increase with the partial pressures of fuel and oxygen. For many types of fuel cells, the power output and the efficiency of the fuel cell stack generally increases with pressure as well. For example, the xe2x80x9cFuel Cell Handbookxe2x80x9d by Appleby, Van Nostrand-Reinhold, 1989, discusses the improvements in power output and efficiency obtained by pressurizing various types of fuel cells including the Phosphoric Acid Fuel Cell (PAFC), the Molten Carbonate Fuel Cell (MCFC), and the Solid Oxide Fuel Cell (SOFC). However, in all cases, this improvement in performance must be paid for by the energy input required to compress the reactants and the increased complexity of the system. In theory, an ideal compressor-expander can pressurize the fuel cell with a minimal energy requirement if the compressor and expander operate at 100% efficiency. In such a system, the fuel cell is pressurized on the air side by a compressor, and the oxygen depleted exhaust gases energize an expander which drives the compressor, requiring very little additional energy input. In practice, component efficiencies become very crucial, and substantial amounts of external energy must be supplied, thereby lowering the improvement in overall system efficiency gained through pressurization. With current technology, this can involve very expensive and bulky machinery. For this reason, in the current state-of-the-art, PAFC""s, MCFC""s, and SOFC""s, are normally operated at atmospheric pressure.
While the advantages and disadvantages of pressurization apply to all fuel cells, they have recently become of prime importance in the Department of Energy xe2x80x9cPartnership for a New Generation of Vehiclesxe2x80x9d (PNGV) program in fuel cells for automobiles where the goal is to obtain a vehicle which will achieve 80 miles/gallon of fuel. Current emphasis in the PNGV fuel cell vehicle program is to use the Proton Exchange Membrane Fuel Cell (PEMFC) since this type offers reduced weight and size, faster start-up, operation at room temperature, and potentially lower cost. Such a fuel cell is normally pressurized to about 3 atmospheres on the air side, and with hydrogen rich gas produced by an on-board gasoline reformer. Kumar (U.S. Pat. No. 5,248,566) calls for PEMFC operating pressures of about 2-5 atmospheres on the hydrogen side. With PEMFC""s in the automotive environment, pressurization is particularly important since the size of the stack must be minimized while the power output maximized. Also, since the PEMFC has a solid fluorocarbon electrolyte which must be humidified in order to function, a sufficiently high water vapor pressure without diluting the hydrogen and oxygen can only be obtained if the system is pressurized. Furthermore, Strasser (U.S. Pat. No. 5,543,238) teaches that recirculating a portion of the humid cathode (oxygen-side) exhaust is beneficial in maintaining the PEMFC electrolyte at the proper moisture level for optimal conductivity. Thus, a critical technology in the success of a fuel-cell-powered automobile is a high efficiency compressor-expander, capable of a wide dynamic range of operation, diffluential discharges, low in cost, low in volume and weight, and capable of controlled recirculation for humidity control. An objective of the present invention is to provide a compressor-expander which can meet these requirements.
Another important area of application of compressor-expanders having diffluential discharge is in turbo-chargers for internal combustion engines. In this application, referring to FIG. 22, pressurized exhaust from the engine typically passes through an expander 83 through inlet conduit 2 before being discharged to the exhaust system of the vehicle through outlet conduit 72. The expander 83 typically drives a compressor 84, through a common shaft 85, which takes suction of fresh air through inlet conduit 3 from the surroundings and discharges into the engine through outlet conduit 74. Heywood in xe2x80x9cInternal Combustion Engine Fundamentals, McGraw-Hill, 1988, states that a typical air discharge pressure is around 2.0 atmospheres. By so increasing the charge of oxygen in the cylinder during combustion, it is possible to burn more fuel per combustion event, and thereby derive more power from an engine at a given rotational speed and with a given displacement volume. In the current state-of-the-art, separate turbines and compressors are used. This equipment is costly and consumes a considerable amount of valuable space. An object of the present invention is to provide a compressor-expander which addresses these deficiencies.
In order to reduce the NOx emissions from internal combustion engines, as much as 30% of the exhaust gas can be recirculated. With conventional turbo-chargers, there has been much interest in incorporating the exhaust gas recirculation (EGR) system with the turbo-chargers. Examples of such attempts include Evans (U.S. Pat. No. 4,249,382), Fortnagel (U.S. Pat. No. 4,956,973) and Kriegler (U.S. Pat. No. 5,131,229). In all of this prior art, bypass valves are used to open conduits connecting the expander discharge with the compressor inlet. Such devices consume space, are costly, and require complex controls. An object of the current invention is to provide a compressor-expander for internal combustion engines which will enable exhaust gas recirculation without complex equipment.
Another important application for compressor-expanders having diffluential discharge is in air-cycle heat pumps. An example of such a system is shown in Ostersetzer (U.S. Pat. No. 5,373,707). Such machines find their greatest application in aircraft where a ready source of high pressure air is available either from by-pass air taken from a compressor-stage of a gas-turbine propulsion engine, or, in the case of supersonic aircraft, from the ram air captured from external aerodynamic surfaces. If an internal space is to be cooled for climate control, as for life support or avionics cooling, a typical arrangement is as follows: referring to FIG. 22, the expander 83 receives high pressure air from one of the said sources, usually after a heat removal process, through conduit 2, and said air expands in the expander 83 doing work and relinquishing its energy. In so doing, it emerges from the expander 83 through conduit 72 with substantially lower energy which is manifested by a greatly reduced temperature. The expander discharge is conducted through conduit 72 into the space for cooling. Said expander 83 drives a compressor 84 through a common shaft 85. Said compressor 84 extracts air from said space through conduit 3 and compresses it. The discharge through conduit 74 from the compressor 84 is generally discharged to the outside, and, in the case of an aircraft, can contribute to the propulsive thrust due to its high kinetic energy if a centrifugal compressor of the proper design is selected.
The compressor-expander can also be used for heating by rearranging the conduits. In such case, the expander 83 receives energy from the high pressure source through conduit 2, but discharges to the outside through conduit 72. Air from the outside is brought to the compressor 84 through conduit 3 which, as before, is driven through a shaft 85 by the expander 83. The air discharging from the compressor 84 through conduit 74 has been energized and therefore emerges hot, by virtue of its increased stagnation temperature. It is therefore conducted to the space to be heated through conduit 74. Air discharged from the heated space is directed to the outside. While the greatest current application for the air-cycle heat pump is with aircraft, one of ordinary skill in the art would know that such equipment could equally be used for other applications and with fluids other than air.
In direct-fluid-contact compressor-expanders, pressure-exchange is the mechanism by which the interface pressure forces between a primary fluid and a secondary fluid enable the primary fluid to do work on the secondary fluid. This process can only exist in a flow which is non-steady in the laboratory frame of reference since pressure forces acting on stationary surfaces can do no work. The work of interface pressure forces, or pressure-exchange, is distinct from the work of turbulent shear stresses. In the latter, a primary fluid of high energy entrains a secondary fluid of lesser energy, and thereby exchange energy through the work of frictional forces exerted at the shear layer. This latter mechanism of direct-fluid-contact energy transfer relies on turbulent mixing between primary and secondary fluids, while pressure-exchange does not involve mixing, notwithstanding the fact that in any real direct-fluid-contact machine, some mixing will inevitably occur. Foa (U.S. Pat. No. 3,046,732) and Garris (U.S. Pat. No. 5,647,221) disclosed new types of ejectors which operate on the pressure-exchange principle as opposed to the turbulent entrainment principle of conventional ejectors. However, these inventions did not disclose means of diffluential separation of primary and secondary fluids prior to discharge from the ejectors. Compressor-expanders of the wave-rotor type, also functioning as a result of pressure-exchange, were invented by Seippel (U.S. Pat. No. 2,399,394), Spalding (U.S. Pat. No. 3,074,620), Berchtold (U.S. Pat. No. 3,012,708), Komaur (U.S. Pat. No. 4,398,868), and Paxson (U.S. Pat. No. 5,267,432). These inventions did permit separate diffluential discharges of primary and secondary. With all of the pressure-exchange compressor-expanders, due to the reversible nature of pressure-exchange, high efficiencies can theoretically be obtained, particularly in comparison with conventional ejectors. Despite much effort on wave rotors, and some success in turbo-charger applications, their complexity has not enabled them to be competitive with conventional compressor-expanders. An objective of the present invention is to provide a compressor-expander with high efficiency by utilizing the advantages of direct-fluid-contact pressure-exchange while maintaining mechanical simplicity and permitting separate discharges of primary and secondary fluids.
Figures of merit on compressor-expander performance, including ejectors, is provided by comparing the performance of a compressor-expander with the ideal-compressor-expander analog. In the ideal-compressor-expander analog, referring to FIG. 22, both expander 83 and compressor 84 operate adiabatically and isentropically. The ideal-compressor-expander analog to an ejector is obtained by conducting an energetic primary fluid through inlet conduit 2 to expander 83, and conducting a lower energy secondary fluid to compressor 84 through inlet conduit 3, and combining the outlet conduits 72 and 74 into one common discharge (not shown). Since real compressor-expanders inevitably include irreversible processes such as mixing and heat transfer, and are therefore not actually isentropic or adiabatic, their performance is poorer than the ideal-compressor-expander analog. However, comparison with the ideal forms a logical basis for which all compressor-expanders, including ejectors, can be judged.
Foa(U.S. Pat. No. 3,046,732) invented an ejector which utilized the benefits of pressure exchange through the use of rotating primary jets. He further showed how the rotating primary jets, when incorporated into a rotor, could be made self-actuating by means of canting the nozzles at an angle with respect to the azimuthal plane. Garris (U.S. Pat. No. 5,647,221) taught how when the working fluid was compressible, shock and expansion wave patterns could be used to advantage in effecting flow induction by pressure-exchange. Garris (U.S. Pat. No. 5,647,221) further taught how pressure-exchange ejectors might effectively be utilized in ejector refrigeration. While these prior art devices offer effective aerodynamic means to provide excellent use of pressure-exchange to affect flow induction, they are deficient in that they require a very high degree of precision in manufacturing to provide the level of sealing necessary while allowing the rotor to spin at the high angular velocities necessary to achieve effective pressure-exchange. Furthermore, in these prior-art pressure-exchange ejectors, the demands on the rotor thrust-bearing are very high due to the high internal supply pressure and the low external suction pressure occurring simultaneously with very high rotor angular velocities. This very demanding combination of requirements for sealing, high rotational speeds, and thrust bearing tend to substantially increase the cost of the device and reduce its potential service life. It is therefore the principal objective of the present invention to provide an ejector which effectively exploits pressure-exchange for flow induction, yet is less demanding with regard to sealing, thrust management, and high rotational speeds. Another objective of the present invention is to provide a pressure-exchange ejector which is simple and economical to manufacture.
After many years of attempts to break the sound barrier, Chuck Yeager in his Bell X-1 aircraft succeeded on Oct. 14, 1947 at achieving Mach 1.06. By 1967, the Lockheed SR-71 Blackbird was in service and flying at sustained speeds exceeding Mach 3.0, while the North American X-15 flew at Mach 7.0 that same year. This rapid advance in high speed aeronautics technology was due to the realization that optimal design for supersonic compressible flow was radically different than that for subsonic flow. While the application of the design principles of supersonic compressible flow are now in common usage in aerospace applications, they have not been effectively applied to pressure-exchange compressor-expanders. An objective of the present invention is to advantageously utilize these principles so as to provide a pressure-exchange compressor-expander which overcomes the aforementioned shortcomings of the prior art.
In the development of new technologies which will enable us to continue to enjoy our prosperity yet preserve the environment, there has been a profound need for high efficiency compressor-expanders in the following technologies:
1. Refrigeration/air conditioning.
2. Gas Turbine engines.
3. Rankine Cycle engines.
4. Turbo-chargers for internal combustion engines
5. Pressurizing units for Fuel Cells.
These are areas of technology whereby improvements can have a major global impact on the amount of the energy we consume and the pollution we create, particularly with regard to greenhouse gases and ozone layer depleting chemicals. Progress in beneficially utilizing direct-fluid-contact ejectors has been hampered by their inherently low efficiency due to the fundamental operating mechanism of turbulent entrainment in the case of conventional ejectors, or by difficulties in mechanical design under the combined requirements of high thrustxe2x80x94high angular velocityxe2x80x94efficient sealing for the case of prior art pressure exchange ejectors. Furthermore, progress in using such devices as compressor-expanders, which maintain the integrity of the primary and secondary fluids at discharge, has been hampered by problems in separating the flows after energy exchange.
The present invention provides a direct-fluid-contact pressure-exchange compressor-expander with diffluential discharge capable of levels of performance comparable with ideal-compressor-expanders while maintaining a degree of simplicity hitherto unavailable in the art. By the use of the principles of supersonic aerodynamics, the mechanical complexity of the prior art pressure-exchange ejectors is reduced, and the demands for sealing and thrust management are significantly assuaged. As a result of the lower stresses and the avoidance of sealing, the pressure-exchange compressor-expander provided herein is capable of operating at extremely high temperatures.
In the instant invention, a primary-fluid comprising a compressible gas or vapor at a high stagnation pressure is introduced through suitable piping to a housing at the location of a primary-fluid inlet conduit. Said primary-fluid is then conducted to a supersonic nozzle whereby it is accelerated to supersonic speeds. As a result of the acceleration, the static pressure of the primary-fluid at the discharge of the nozzle is substantially reduced. The primary flow will then impinge upon canted vanes fixedly attached to a free-spinning rotor, thereby causing the rotor to spin at a high rotational speed. Over the wedge-shaped vanes, oblique shock structure will form, creating a series of expansion fans and compression waves which will force the secondary fluid to expand into the interstices between the peripherally spaced oblique vane-shock structures and behind the vanes. A secondary-fluid is introduced to the said housing through suitable piping and then conducted to the vicinity of the nozzle discharge. An aerodynamic shroud further directs the secondary fluid into the vicinity of the rotor vanes and associated shock and expansion fan structure. Momentum will be exchanged between the primary-fluid and the secondary-fluid at the interfaces between said primary fluid and said secondary fluid through pressure-exchange. It is known that the pressure-exchange process occurs very rapidly after primary and secondary fluids come into contact. Normally, the pressure-exchange process is complete after a downstream distance of about 5 rotor-vane widths. After pressure-exchange occurs, the primary and secondary fluid can either be mixed and diffused to subsonic speeds before being transported to the mixed-fluid outlet conduit, or they can be separated diffluentially. In the former case, the compressor-expander is called a xe2x80x9cpressure-exchange ejectorxe2x80x9d. In the latter case, the device is a generic xe2x80x9cpressure-exchange compressor-expanderxe2x80x9d. Thus, the pressure-exchange ejector may be regarded as the special case of the pressure-exchange compressor-expander whereby the de-energized primary fluid discharge and the energized secondary fluid discharge are combined, mixed, and directed to a common unifluential discharge port. In the case of the pressure-exchange ejector, at the discharge, the specific energy, and stagnation pressure, of the mixed discharge flow will be greater than that of the secondary flow, but less than that of the primary flow. This energized and compressed unifluential mixed-fluid may now be used for its intended application.
In the generic case of the pressure-exchange compressor-expander, the de-energized primary fluid can be discharged separately from the discharge of the energized secondary fluid thereby providing diffluential discharge. This separation is possible in the present invention since the pressure-exchange process occurs very rapidly as the primary fluid and the secondary fluid come into contact in the supersonic wake regions behind the vanes and undergo a mutual deflection to a common orientation in the rotor frame of reference. During this process, very little mixing or heat transfer occurs. Since following the pressure-exchange process, both primary and secondary fluids are in direct contact with each other, some mixing is inevitable. However, if the separation is affected shortly after completion of the pressure-exchange process, both primary fluid and secondary fluid can. maintain substantial integrity. In the present invention, the rotor can be conceived of consisting of three rigidly connected sections, each a body which is revolute about the rotor""s axis of rotation. Typically, all sections would be integrally fabricated with the rotor, but one could easily fabricate them separately and join them in a manner such that during operation, they do not pivot relative to one another. However, one of ordinary skill in the art might introduce azimuthal adjustability between sections. Furthermore, the desirability of having means for making adjustment during operation in some applications is anticipated in the present invention. The first section is the vaned section where supersonic shock and expansion fans are established by the use of vanes in order to create rotating interstices into which the secondary fluid will penetrate. The second section of the rotor is the pressure-exchange section and is where pressure-exchange is allowed to take place. The third section is the selective deflection section where either primary fluid or secondary fluid, or a combination thereof, can be diverted into its own plenum. The combination of primary and secondary fluids that are deflected after pressure-exchange in said deflection section are herein termed xe2x80x9cfirst-fluidxe2x80x9d. The remaining combination of primary and secondary fluid that is not deflected after pressure-exchange is herein termed xe2x80x9csecond-fluidxe2x80x9d. A basic concept of the invention is that at the conclusion of the pressure-exchange phase, in the rotor frame of reference, the primary fluid and the secondary fluid move in a common direction, which in general is different from the vane canting angle, and have the same static pressure, although, in general, different speeds, temperatures, densities, entropies, etc. In order to efficiently separate primary and secondary fluids, or to produce a predetermined combination of the two, the deflectors must be precisely located and the geometry of the deflectors and the passages there between must be precisely configured for the application. For maximum separation, the number of deflectors should precisely correspond to the number of vanes, and the azimuthal relationship between the deflectors and the vanes must precisely correspond to the trajectories of the respective primary and secondary fluid streams. The widths of the deflectors and the passages there between must correspond to the cross-sections of the respective fluid streams. The number and shape of vanes, and the corresponding shape and location of the deflectors, would be determined by one skilled in the art based on the design requirements for pressure ratio, working fluids, maximum allowable rpm, primary and secondary flow rates, and primary and secondary fluid temperatures and densities. In the case of the pressure-exchange ejector, integral rotor sections for the second and third sections are not needed.
It has been noted previously that for certain applications such as turbocharging of internal combustion engines and in fuel cell pressurization, controlled combining of primary and secondary fluid streams may be desirable. In the former case, the purpose is to recirculate exhaust gas in order to reduce NOx formation, and in the second case, the purpose is to conserve moisture in the fuel cell. In the present invention, this can easily be achieved by either reducing or increasing the number of deflection vanes, changing their widths, or changing their azimuthal phase relationship with regard to the vanes. Thus for example, let us consider maximum separation. For maximum separation, the number of vanes and the number of deflectors are equal, and the deflectors are azimuthally phased with respect to the vanes at an optimal angle determined by the locations of the respective fluid streams and sized such that all of either primary fluid or secondary fluid is deflected (depending on the design). The passages between the deflectors are configured to allow all of the secondary fluid to pass if all of the primary fluid were deflected, or, alternatively, the passages are configured to allow all of the primary fluid to pass if all of the secondary fluid were deflected. If the deflectors were not phased azimuthally by said optimal angle, but rather by a predetermined azimuthal displacement angle, then perfect separation would not occur resulting in some combining of primary and secondary fluids. Similarly, if the deflector vanes were of a width that did not deflect all of the primary fluid, then combining would occur. A third method of producing a predetermined amount of combining of primary and secondary fluid at discharge would be simply to have a different number of deflectors than vanes; for example, if a fraction of the deflectors were omitted, then a fluid-stream that would have been deflected would then discharge with its counterpart fluid-stream, and combining would occur. Similarly, if there were an excess of deflectors in comparison with the vanes, counterpart fluid-streams would be mixed. Hence, the invention admits to a variety of methods of producing predetermined combining of primary and secondary fluids.
Note that in the current context, the word xe2x80x9ccombiningxe2x80x9d means allowing primary and secondary flows to merge together and to be conducted in a common flow path. The word xe2x80x9cmixingxe2x80x9d is taken to mean xe2x80x9ccombiningxe2x80x9d at a more intimate level, such as the Kolmagorov turbulence scale, or even the molecular scale. As a result of molecular diffusion and turbulence, for gases or vapors, a xe2x80x9ccombinedxe2x80x9d flow will become a xe2x80x9cmixedxe2x80x9d flow if sufficient time is allowed for these processes to occur. In the present invention, substantial mixing occurs only after the fluid streams pass the rotor.
A prime advantage of the supersonic flow design of this invention is that the complex rotational seals between the primary and secondary flows that are required in the prior art pressure-exchange ejectors are not needed, so that the instant pressure-exchange ejector is not sensitive to the effects of the thermal or centrifugal expansion of the rotor. Furthermore, it should be noted that in this invention, the flow over the surface of the rotor remains supersonic, hence the static pressure on the surface of the rotor is relatively low. This provides a substantial benefit in reducing the axial thrust load on the rotor, which, again, simplifies the manufacture, increases the service life, and reduces the cost. This invention permits the use of an abundant selection of materials and manufacturing methods for the fabrication of the various components. The most critical component is the rotor where centrifugal stresses and dynamic balance must be taken into account. Satisfactory rotors can be fabricated by CNC machining, casting, injection molding, powder metallurgy techniques, 3-D printing, and other methods. The supersonic design of the pressure-exchange compressor-expander herein disclosed greatly simplifies the manufacture of the ejector, increases the service life, and reduces the cost.
This disclosure further provides a pressurization system for fuel cell power plants which is particularly useful for automotive applications using PEM fuel cells. The disclosure recited herein has a compressor-expander which is powered by exhaust gases from the fuel cell and discharges said exhaust gas to the atmosphere. Said compressor-expander receives clean secondary air from the ambient and compresses it for discharge into the secondary inlet of a pressure-exchange ejector. The primary of said ejector is steam provided from a boiler. The steam provides the excess energy needed to make up for inherent losses, and it also provides needed moisture for the fuel cell. The disclosed system can be more compact than comparable compressor-expander-motor combinations utilizing conventional machinery.
Also disclosed in this invention is a novel turbo-charger for use in internal combustion engines using the pressure-exchange compressor-expander. This system is particularly useful for automotive applications where space, weight, and cost are critical.
Also disclosed in this invention is a novel air-cycle heat pump utilizing the pressure-exchange compressor-expander. Said heat pump is particularly useful for aircraft applications where a ready source of compressed air is available, space consumption and weight must be minimized, and high reliability is essential.